The present invention relates to a camera apparatus and, more particularly to a 3-chip color video camera having a vertical detail enhancement function, for example.
3-chip video cameras have hitherto been known as color video cameras. A 3-chip video camera includes a dichroic prism disposed behind a camera lens for analyzing incident light from an object to provide three primary colors R (red), G (green), B (blue). Three solid-state imaging devices of the same size are disposed at the positions in which light rays thus analyzed by the dichroic prism are focused. The R, G and B color signals are respectively obtained from outputs of the three solid-state imaging devices.
According to this system, since optical paths of three primary colors R, G and B are independent, it is possible to freely correct colors by using filters, called trimming filters, disposed on the optical paths. As a consequence, optimal imager characteristics can be obtained with ease and reproduced color images will have satisfactory tonal value.
Recently, in order to compensate for deterioration in responses of a solid-state imaging device or to enhance sharpness, horizontal and vertical detail enhancement (compensating) processing has become available.
In particular, vertical detail enhancement processing uses a method called the RGB pixel shift method or the RGB image shift method. By way of example, when a detail is enhanced by using the R signal and the G signal (referred to hereinafter simply as "RG detail") for example, according to the RGB image shift method, the positions of R-channel and G-channel solid-state imaging devices are shifted by one pixel pitch (i.e., one line amount) relative to the reference position of B-channel solid-state imaging device.
Specifically, when the solid-state imaging devices are bonded to the dichroic prism, the B-channel solid-state imaging device is bonded to the prism such that the center of its image region is aligned with an optical axis of the prism for the color blue. The R-channel and G-channel solid-state imaging devices are bonded to the dichroic prism such that centers thereof are respectively shifted in the amount of one line in the vertical direction from the corresponding red and green optical axes of the prism, thereby realizing the RGB image shift method corresponding to the RG detail.
A principle of RG detail processing will be described with reference to FIG. 1 which shows an imager model in a CCD (charge-coupled device) solid-state imaging device of a FIT (frame interline transfer) system.
As shown in FIG. 1 of the accompanying drawings, a mark is picked up by imager portions of the R-channel and the G-channel at their imager regions at a position ranging from the Nth line to the N+3th line. Meanwhile, because the B-channel solid-state imaging device is shifted downwards by one line in the vertical direction, relative to the R-channel and G-channel solid-state imaging devices, the B-channel imager portion will pick up the same mark on its imager region at a position ranging from the N+1th line to the N+4th line.
During the next vertical blanking period, the signal charge thus picked up is transferred from the imager portion to the storage portion. The storage portions of the R-channel and the G-channel store signal charges corresponding to the mark at a position from the Nth line to N+3th line. The storage portion of the B-channel stores signal charges corresponding to the mark at a position from the N+1th line to N+4th line.
As a consequence, during the next effective horizontal scanning period, a signal charge of every line is transferred to a horizontal register at every horizontal blanking period. Due to the position of the image data picked up by the R-channel solid-state imaging device and the G-channel solid-state imaging device, these image data are read out earlier than image data picked up by the B-channel solid-state imaging device by one horizontal scanning period (1H). The R-channel and G-channel solid-state imaging devices output signals of -1H relative to an output signal of the B-channel solid-state imaging device.
The RG detail signal processing will be described below. The RG detail signal processing is effected by a detail enhancement circuit shown in FIG. 2. As shown in FIG. 2, the detail enhancement circuit is composed of two 1H delay circuits {circuits-for delaying signals by one horizontal scanning period: first 1H delay circuits (101R, 101G) and second 1H delay circuits (102R, 102G)} connected in series to imager signal lines for carrying out a detail enhancement processing (detail processing). The detail enhancement circuit further includes 3-input adding circuits (103R, 103G) connected to the 1H delay circuits 102R, 102G and amplifiers 104R, 104G). The amplifiers 104R, 104G have a gain of 2, and are connected between junctions (aR, aG) of the first 1H delay circuits (101 R, 101 G) and the second 1H delay circuits (102R, 102G) and the 3-input adding circuits (103R, 103G).
An R signal Sr(-1) of -1H is supplied to the first 1H delay circuit 101R from the preceding stage R-channel solid-state imaging device 105R through a contact bR of the preceding stage. An R signal Sr(0) of 0H from the first 1H delay circuit 101R is supplied to the second 1H delay circuit 102R. The R signal Sr(-1) of -1H from the contact bR and an R signal 2Sr(0) of 0H whose signal level was amplified by a factor of two by the amplifier 104 are supplied to the 3-input adding circuit 103R. An R signal Sr(1) of 1H from the second delay circuit 102R also is supplied to the 3-input adding circuit 103R. The 3-input adding circuit 103R calculates [2Sr(0)-(Sr(-1)+Sr(1))] to output a detail enhanced R signal dSr. This detail enhanced R signal dSr is output at an output terminal 106Ra of the 3-input adding circuit 103R.
FIG. 3 shows changes in the waveforms of signals obtained when the detail enhancement processing is carried out. The normal R signal Sr(0) of 0H is delivered to an output terminal 106Rb through a main signal line 107R led out from the contact aR.
In the G-channel, similarly, a G signal Sg(-1) of -1H is supplied to the first 1H delay circuit 101G from the preceding stage G-channel solid-state imaging device 105G through a contact bG of the preceding stage. A G signal Sg(0) of 0H from the first 1H delay circuit 103 is supplied to the second 1H delay circuit 102G. The G signal Sg(-1) of -1H from the contact bG and a G signal 2Sg(0) of 0H whose signal level was amplified by a factor of two by an amplifier 104G are supplied to a 3-input adding circuit 103G. Further, a G signal Sg(1) of 1H from the second delay circuit 102G also is supplied to the 3-input adding circuit 103G.
The 3-input adding circuit 103G calculates [2Sr(0)-(Sr(-1)+Sr(1))] to output a detail enhanced G signal dSg. This G signal dSg is output at an output terminal 106Ga of the 3-input adding circuit 103G. The normal G signal Sg(0) of 0H is delivered to an output terminal 106Gb through a main signal line 107G led out from the contact aG.
In the B-channel, a B signal (B signal of 0H) Sb(0) from the B-channel solid-state imaging device 105B is delivered to an output terminal 106Bb through a main signal line 107B without detail enhancement processing.
As described above, in the detail enhancement circuit, the two 3-input adding circuits 103R and 103G output the detail enhanced R signal dSr and the detail enhanced G signal dSg. The normal R signal Sr(0) of 0H, the normal G signal Sg(0) and the normal B signal Sb(0) are output from the main signal lines 107R, 107G and 107B, respectively. Therefore, it becomes possible to compensate for deterioration of response in the high frequency band in the solid-state imaging device.
In the detail enhancement processing, however, the solid-state imaging device(s) (e.g. 105R, 105G or 105B) for outputting the color signals to be detail-enhanced are mechanically bonded to the dichroic prism at a physical position shifted by one pixel pitch relative to a corresponding position for a solid-state imaging device for outputting a color signal which is not detail-enhanced or in an opposite positional relationship. Because the position of mechanical bonding determines which color signals may be detail-enhanced, the set of color signals which can be detail-enhanced is limited to one form when the camera apparatus is designed or manufactured.
Specifically, when the form of the RG detail shown in FIGS. 1 and 2 is changed to RGB detail form or G detail form, for example, the solid-state imaging devices 105R, 105G and 105B that had been bonded to the dichroic prism would have to be detached and bonded again to the dichroic prism at positions conforming to the desired detail form. Therefore, to change the detail form is very difficult and the selection of the detail form is limited accordingly.
To solve the above-mentioned problem, it is proposed to exchange the entire CCD block to thereby change between various detail forms. Under this proposal, there would be a multiplicity of CCD blocks, prepared in advance, in which the solid-state imaging devices are bonded to the dichroic prism according to each kind of detail form.
There are however seven detail forms, i.e., R, G, B, RG, RB, GB and RGB. Therefore, seven CCD blocks would need to be kept in stock in order to cope with the change of detail form. This would take much time and labor and would make the camera apparatus very expensive. Moreover, even when the solid-state imaging devices are mechanically bonded to the dichroic perish by an automation system, in order to manufacture the seven CCD blocks, a very small positional displacements must be accommodated. For instance, small positional displacements, such as one line amount of the imager region, would have to be determined and the solid-state imaging devices would have to be bonded to the dichroic prism with great accuracy in order to properly account for these small positional displacements. As a result, the manufacturing process becomes complex, the number of processes is increased and the manufacturing cost is increased.